A heat exchanger with a pair of tanks made to communicate with each other via a plurality of flat tubes is often used as a condenser that cools a high-pressure coolant. Heat exchangers used in such applications in the known art include those adopting a junction structure whereby the ends of the flat tubes are inserted and brazed at tube insertion holes formed at the tanks with the openings of the tube insertion holes extending along the direction of the radius of the tanks so as to allow the surfaces of the flat tubes with a relatively large area to turn toward the adjacent tubes (see, for instance, patent reference literature 1 and 2). In this structure, the inner diameter of the tanks is set equal to or greater than the width of the tubes along the direction in which the tank axes extend (hereafter referred to as the tube width).
A heat exchanger with the inner diameter of the tanks thereof set equal to or greater than the tube width as described above, may be used in conjunction with a high-pressure coolant such as CO2. In such a case, the wall thickness of the side walls of the tanks must be increased to assure greater strength which, in turn, results in a relative increase in the external dimensions of the tanks. This ultimately leads to a problem in that the heat exchanger becomes unnecessarily large and heavy.
The problem described above is addressed in a structure that includes communicating portions as well as a distribution area ranging along the axial direction relative to the tanks with the communicating portions each assuming a shape gradually widening, starting from the distribution area toward the tube insertion hole until its width becomes substantially equal to the tube width, so as to allow the tanks to assume a smaller inner diameter at the distribution areas thereof relative to the tube width, as disclosed in patent reference literature 3.
Patent reference literature 1: Japanese Unexamined Patent Publication No. H8-145591
Patent reference literature 2: Japanese Unexamined Patent Publication No. 2001-133076
Patent reference literature 3: Japanese Unexamined Patent Publication No. 2003-314987